Protein kinases represent a large family of proteins which play a central role in the regulation of a wide variety of cellular processes, maintaining control over cellular function. A partial list of such kinases includes abl, AKT, bcr-ab1, Blk, Brk, Btk, c-kit, c-met, c-src, c-fins, CDK1, CDK2, CDK3, CDK4, CDK5, CDK6, CDK7, CDK8, CDK9, CDK10, cRaf1, CSF1R, CSK, EGFR, ErbB2, ErbB3, ErbB4, Erk, Fak, fes, FGFR1, FGFR2, FGFR3, FGFR4, FGFR5, Fgr, flt-1, Fps, Frk, Fyn, GSK3α, GSK3β, Hck, IGF-1R, INS-R, Jak, KDR, Lck, Lyn, MEK, MK2, MSK1, p38, PDGFR, PIK, PKB, PKA, PRAK, PRK2, PKC, PYK2, P70S6, ROCK2, ros, tie, tie2, TRK, Yes, and Zap70. Inhibition of such kinases has become an important therapeutic target.
AKT (also known as protein kinase B (PKB) or Rac-PK-beta), and its gene family products, has been identified as a serine/threonine protein kinase. Testa et al., Proc. Natl. Acad. Sci., 2001, 98, 10983-10985; Lawlor et al., J. Cell Sci., 2001, 114, 2903-2910; Duan, Circ. Res., 2000, 86, 15-23. Three isoforms of PKB are currently known, PKBα (AKT1), PKBβ (AKT2), and PKBγ (AKT3). Cheng, Proc. Natl. Acad. Sci. USA, 1992, 89, 9267-9271; Brodbeck, et al., J. Biol. Chem. 1999, 274, 9133-9136. PKB mediates many effects of IGF-1 and other growth factors on tumor growth and inhibition of apoptosis. Nicholson, et al., Cell. Signal., 2002, 14, 381-395. PKB plays an important role in cell proliferation, apoptosis and response to insulin. For these reasons, modulation of PKBs is of interest in the treatment of tumorigenesis, abnormal cell proliferation, and diabetes.
The molecular structure of the PKBs comprises a regulatory site near the carboxy terminus of the polypeptide, a catalytic domain with an activation loop having a threonine, and an amino-terminal pleckstrin homology domain. The pleckstrin homology domain permits anchorage of the enzyme to the cell membrane through interaction with phospholipids, which triggers the activation of the PKBs. The role of pleckstrin homology domain requires phosphorylation of phosphatidylinositol at the D-3 position via phosphatidylinositol 3-kinase PI3K, an SH2 domain protein that associates with activated receptor tyrosine kinases, particularly IGF-1R. In particular, phosphoinositol-3-kinase, when activated by receptor tyrosine kinase, catalyzes the synthesis of phosphoinositol-3,4-diphosphate and phosphatidylinositol 3,4,5-triphosphate. The pleckstrin homology domain binds 3-phosphoinositides, which are synthesized by PI3K upon stimulation by growth factors such as platelet derived growth factor (PDGF), nerve growth factor (NGF) and insulin-like growth factor (IGF-1). Kulik et al., Mol. Cell. Biol., 1997, 17, 1595-1606; Hemmings, Science, 1997, 275, 628-630; Datta, et al. Genes Dev., 1999, 13, 2905-2927. Lipid binding to the pleckstrin homology domain promotes translocation of PKB to the plasma membrane. Further activation of PKB occurs by phosphorylation by another protein kinase, PDK1 at Thr308, Thr309, and Thr305 for the PKB isoforms 1, 2 and 3, respectively. A third step of activation is catalyzed by a kinase that phosphorylates Ser473, Ser474 or Ser472 in the C-terminal tails of PKB/AKT-1, -2 and -3 respectively. The Ser473 kinase activity has been identified to be associated with plasma membrane and is not due to PKB and PDK1 kinase activity. Hill et al., Current Biology, 2002, 12, 1251-1255; Hresko et al., J. Biol. Chem., 2003, 278,21615-21622. The process produces the fully activated form of PKB.
Activation of PKB can also occur by inhibiting the D-3 phosphoinositide specific phosphatase, PTEN, which is a membrane-associated FYVE finger phosphatase commonly inactivated in many cancers, including prostate cancer. Besson, et al., Eur. J. Biochem., 1999, 263, 605-611; Li, et al., Cancer Res., 1997, 57, 2124-2129.
The catalytic domain of PKB is responsible for the phosphorylation of serine or threonine in the target protein.
Once activated, PKB mediates several cellular functions including proliferation, cell growth, and promotion of survival. Intracoronary, adenovirus-mediated akt gene transfer in heart limits infarct size following ischemia-reperfusion injury in vivo. Miao et al., J. Mol. Cell. Cardiol., 2000, 32, 2397-2402. The antiapoptotic function of PKB is reported to be mediated by its ability to phosphorylate apoptosis regulatory molecules including BAD, caspase 9, IKK-, and the forkhead transcriptional factor FKHRL1. Datta et al., at 2905. PKB signaling is also implicated in the physiological regulation of organ size (Verdu, et al., Nat. Cell Biol., 1999, 1, 500-506), glucose homeostasis (Czech, et al., J. Biol. Chem., 1999, 274, 1865-1868), vasomotor tone (Luo, et al. J. Clin. Invest. 1999, 106, 493-499), and angiogenesis (Kureishi, et al., Nat. Med., 2000, 6, 1004-1010).
Manifestations of altered PKB regulation appear in both injury and disease, the most important role being in cancer. PKB kinase activity is constitutive activated in tumors with PTEN mutation, PI 3-kinase mutation and overexpression, and receptor tyrosine kinase overexpression. PKB is also a mediator of normal cell functions in response to growth factor signaling. Expression of the AKT gene was found to be amplified in 15% of human ovarian carcinoma cases. Cheng, et al., Proc. Natl. Acad. Sci. U.S.A., 1992, 89, 9267-9271. AKT has also been found to be over expressed in 12% of pancreatic cancers. Cheng, et al., Proc. Natl. Acad. Sci. U.S.A., 1996, 93, 3636-3641. In particular, AKT-2 is over-expressed in 12% of ovarian carcinomas and in 50% of undifferentiated tumors, suggesting that PKB may be associated with tumor aggressiveness. Bellacosa, et al., Int. J. Cancer, 1995, 64, 280-285. PKB is also a mediator of normal cell functions. Khwaja, Nature, 1999, 401, 33-34; Yuan, et al., Oncogene, 2000, 19, 2324-2330; Namikawa, et al., J Neurosci., 2000, 20, 2875-2886.
Elucidation of the role of PKB in the increase of growth and inhibition of apoptosis is complicated by the many protein substrates of PKB, including BAD, Forkhead (FOXO family), GSK3, Tuberin (TSC2), p27 Kip1, p70S6k, protein kinase C-, forkhead in rhabdomyosarcoma, Raf, cAMP-response element-binding protein, glycogen synthase kinase-3, mTOR, and the androgen receptor. Lin, et al., Proc. Natl. Acad. Sci. U.S.A., 2001, 98, 7200-7205; Blume-Jensen, et al., Nature 2001, 411, 355-365; Vivanco, et al., Nat. Rev. Cancer, 2002, 2, 489-501.
The various PKBs vary in their abundance in different mammalian cell types. For example, PKBβ are especially abundant in highly insulin-responsive tissues, including brown fat.
Modulation of PKB by small molecules can be achieved by identifying compounds that bind to and activate or inhibit one or more PKBs. Cao et al. in United States Publication No. 2004/0122016, published Jun. 24, 2004, disclose certain thiophene derivatives and thiophene analogs as inhibitors of protein kinases. In particular, the disclosure addresses compositions effective as inhibitors of Rho-associated coiled-coil forming protein serine/threonine kinase (ROCK), extracellular signal regulated kinase (ERK), glycogen synthase kinase (GSK), and members of the AGC sub-family of protein kinases. Id. at 4. The AGC sub-family of kinases includes protein kinase A (PKA), PDK, p70S6K-1, p70S6K-2, and PKB. Id.
Triciribine has been reported to inhibit cell growth in PBKβ overexpressing cells, transformed cells, and was effective at a concentration of 50 nM. Yang et al., Cancer Res., 2004, 64,4394-4399.
In other work, U.S. Pat. No. 3,904,756, issued Sep. 9, 1975, discloses substituted nitroimidazolyl thiadiazoles and oxadiazoles as antibacterial agents and growth promoting compounds. The patent does not address modulation of PKB.
U.S. Pat. No. 5,086,053, issued Feb. 4, 1992, discloses certain derivatives of 1,3,4-thiadiazole, a method of obtaining them, and pharmaceutical compositions containing them. The agents are described as muscarinic cholinergic agonists. Id. at col. 2, 11. 6-7. The '053 patent, however, does not disclose modulators of PKB.
Derivatives of 1,3,4-oxa(thia)diazolopyrimidin-5-ones, and related compounds, were synthesized. Yadav et al., Synthesis, 2003, 1, 63-66. Several derivatives of thiazolopyridopyrimidines and thiazolo-thiadiazolopyrimidines were synthesized by Singh and colleagues, and tested for anti-fungal activity. Singh et al., Indian J. Chem., 1994, 33B, 350-354. Derivatives of 2-amino-1,3,4-thiadiazole, and related compounds, have been synthesized and tested for anesthetic activity. Mazzone et al., Il Farmaco, 1993, 48, 1207-1224. Some derivatives of thiadiazoles were synthesized and tested for antimicrobial activity. Pachhamia et al., J. Inst. Chemists (India), 1989, 61, 54-56. Moreover, synthesis of acetamide derivatives of 1,3,4-thiadiazoles, and related compounds, have been reported. Shah et al., J. Indian Chem. Soc., 1982, LIX, 678-680.. None of the above references disclose modulation of PKB.
Anti-tumor effects of some 1,3,4-thiadiazole derivative(s) have been reported. Platonova, Akad Med Nauk, SSSR 2, 167, as cited by Shah et al. at 678.